An anti-racism campaigner spent a year infiltrating the fringes of the white nationalist alt-right, and saw the real-world effects of extremist online ideology in Charlottesville.

Patrik Hermansson had thought the day's drama was over.

He had arrived at Emancipation Park in Charlottesville, Virginia, early in the morning of 12 August 2017.

There he joined a group of far-right and alt-right activists who were protesting against the removal of a statue of a Confederate US Civil War leader, Robert E Lee.

He found himself at the centre of an angry protest when the gathering was declared unlawful and armed alt-righters were marched out of the park by police. He witnessed scuffles and was sprayed with mace by an anti-fascist counter-protester. After a walk to another venue outside the city, it was time for some rest.

"I switched out of my clothes and walked back into town," he says. "I was just out getting lunch when I saw this big demonstration walk past."

These protesters were marching in opposition to the white nationalist and alt-right gathering in the park. Patrik stopped to watch.

That's when a car drove straight into the crowd.

"It ploughed through the demo and stopped five or 10 metres away from me," he says. "And then everything happened after that."

One woman, Heather Heyer, was killed by the car, and 35 others were injured. A man facesmurder and other charges in connection with the attack.

The violence in Charlottesville that day drew new attention to the rising subculture of the alt-right - an amorphous collection of nationalists, traditionalists, race obsessives, hardcore Trump supporters and others who found each other online. They are a subgroup of the wider far right and often claim to be a new political vanguard, although critics say they are nothing but fascists who have learned how to use social media.

And Patrik Hermansson was well-placed to make sense of the events in Charlottesville and their wider impact. By then he had been undercover in the alt-right - in the UK, Europe and the US - for a year.